Method of manufacturing an inductive ballast

ABSTRACT

The invention relates to a method of manufacturing an inductive ballast for a low-pressure mercury vapor discharge lamp. A block of elastically deformable synthetic material which swells in vacuo is urged against the connecting conductors of the coil in the ballast. Subsequently the air in the space around the coil is conducted away so that the block will expand to envelope the connecting conductors. Subsequently an insulating moulding mass is provided around the coil and around the connecting conductors which are surrounded by the synthetic resin.

United States Patent Van Der Hoek [451 Sept. 2, 1975 1 1 METHOD OFMANUFACTURING AN INDUCTIVE BALLAST [75] Inventor: Jan Lambertus Van DerHock,

Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New

- York, NY.

[22] Filed: Dec. 29, 1971 [21] Appl. No.: 213,448

[30] Foreign Application Priority Data Jan. 13, 1971 Netherlands 7100411[52] US. Cl. 264/46.5; 264/45; 264/101; 264/272; 336/96; 338/248 [51]Int. Cl... B29d 27/04; HOlf 41/12; HOlc 17/00 [58] Field of Search336/96; 264/45, 46, 101, 264/272 [56] References Cited UNITED STATESPATENTS 3,153,694 10/1964 Tomlinson 264/45 X 3,163,838 12/1964 Antoliset al. 336/96 X 3,240,848 3/1966 Burke et a1. 336/96 X 3,305,614 2/1967Parsons 264/101 X 3,319,203 5/1967 Haughney 336/96 3,484,510 12/1969Corazza 264/101 X 3,515,799 6/1970 Ristuccia et a1. 264/45 X 3,639,5672/1972 Herrig 264/45 OTHER PUBLICATIONS DAS 1,132,712, July 1962,Chemische Werke Huels A/G.

Primary Examiner-H. S. Cockeram Attorney, Agent, or FirmFrank R.Trifari', David R. Treacy [5 7] ABSTRACT 3 Claims, 10 Drawing Figures ISEP 2x975 1903,22?)

saw 2 [IF 3 PATENTED 2|975 3,903,223

SHEET 3 UF METHOD OF MANUFACTURING AN INDUCTIVE BALLAST The inventionrelates to a method of manufacturing an inductive ballast which isprovided with a coil and a housing enveloping said coil and electricalconductors for connection of the coil. A part of the combination of thecoil and the part of the connection conductors located within thehousing is covered by a synthetic resin which is provided with closedcells. The space between the combination of coil and conductors and thewall of the housing is filled for the greater part with an insulatingmoulding mass.

When manufacturing an inductive ballast for stabilizing a discharge in adischarge lamp an insulating moulding mass has been known to be used. Apolyester mixed with sand which is moulded around the coil of thisarrangement is known. In this process the coil is first placed in ahousing and then the interior is evacuated through several smallapertures in said housing and subsequently the polyester mass can flowinto the housing through a second aperture and then hardens. Anadvantage of this known ballast is that the coil is satisfactorilyinsulated and that the heat from the coil is satisfactorily conductedaway to the outer wall of the enveloping housing.

A drawback of these known ballasts is, however, that the moulding mass,for example, the polyester mass may crack due to shrinkage in the courseof time. If these shrinkage cracks occur at areas where electricalconductors are present which extend from the coil to the exterior of thehousing, a pressure may be exerted on these supply conductors such thatthey become defective. As a result the inductive ballast may be cut outof the circuit and cannot further operate.

It is also known to manufacture devices with a synthetic resin providedwith closed cells such as described above. This material is providedbetween the insulating moulding mass and parts of the electric unit.See, for example, Swiss Patent Specification No. 316936. A drawback ofthe device described in this Swiss Patent Specification is, however,that a fairly large part of the coil is surrounded by the syntheticresin with its closed cells. This affects the conducting away of heatfrom this coil.

It is an object of the present invention to provide a method of the kinddescribed in the introduction above, in which on the one hand theinfluence of possible shrinkage cracks in the hardened insulatingmoulding mass, which might lead to breakage of the electrical conductorsin the ballast, is prevented and in which furthermore the resin havingclosed cells used for this purpose is provided in a very simple manneraround the electrical connecting conductors, and in which the conductingaway of heat from the coil of the finished ballast is satisfactory.

According to the invention a method of manufacturing an inductiveballast which is provided with a coil and a housing enveloping said coiland electrical conductors for the connection of the coil, in which atleast a part of the combination of the coil and the part of theconnecting conductors located within the housing is covered by asynthetic, resin which is provided with closed cells, and in whichsubsequently the space between the said combination of coil andconnecting conductors on the one hand and the wall of the housing on theother hand is filled for the greater part with an insulating mouldingmass is characterized in that a block of a mainly elastically deformablesynthetic resin is laid on the connecting conductors, the housing beingsubsequently substantially closed in such a manner that the spacebetween these conductors and the adjacent wall of the housing is atleast for a great part filled with the synthetic resin block. Theinterior of the housing is subsequently substantially evacuated so thatthe of synthetic resins swells and envelops the connecting conductors.The moulding mass is then admitted in a liquid state to the interior ofthe housing and hardens in the housing.

An advantage of this method is that the synthetic resins can be providedin a very simple manner around the connecting conductors. In this caseuse is made of the known evacuation of the housing so as to enable themoulding mass to flow in. When the synthetic resin block swells uponevacuation it will envelop the con necting conductors. This advantagewould not be adequately achieved with a sleeve of an insulating materialprovided around the connecting conductors. In fact, then the mouldingmass could also creep between the connecting conductors and the sleeveupon evacuation of the interior of the housing.

The method according to the invention may be used, for example, for themanufacture of an inductive ballast for stabilizing the discharge in adischarge lamp, for example, a low-pressure mercury vapor dischargelamp. The use of such a method for other ballasts such as, for example,transformers is also possible.

It is feasible that each part of the synthetic resin block be built upin the same manner. In that case the block of synthetic resin will tendto swell in all directions to an equal extent during evacuation of thehousing because originally air of atmospheric pressure prevailed in theclosed cells.

In a farther embodiment according to the invention the side of the blockof synthetic resin remote from the connecting conductors is notexpandable and the support for the conductors is provided on the side ofthem which is remote from the synthetic resin block prior to providingthe housing.

An advantage of this method is that the side of the block of syntheticresin facing the conductors swells to a greater extent than the partwhich is remote from the conductors. As a result the block tends toassume a curved shape with its convex side facing the connectingconductors. Of advantage is that the connecting conductors are morefirmly urged against the support which is on the other side of theseconductors. Thus the conductors are adequately enveloped by thedeformable synthetic resin, and the conductors are satisfactorilyabutted against the support.

In a further method according to the invention the side of the syntheticresin block remote from the connecting conductors does not have anystretching properties, and the side of the synthetic resin block facingthe connecting conductors is provided with a plurality of groovesparallel to the connecting conductors, the number of grooves being equalto the number of connecting conductors. The grooves are opened bycurvature of the synthetic resin block during evacuation in such amanner that they can accommodate the connecting wires and closing againafter flowing of the moulding mass, thus enveloping the connectingconductors.

An advantage of this method is that the connecting conductors aresurrounded by the deformable synthetic resin block even moreeffectively. A further advantage is that a support on the other side ofthe connecting conductors is not necessary in this case.

In order that the invention may be readily carried into effect, someembodiments thereof will now be described in detail by way of examplewith reference to the accompanying diagrammatic drawing in which:

FIG. 1 is a perspective view of a cover for a housing of a ballastaccording to the invention;

FIG. 2 is a perspective view of a ballast according to the inventionduring a given manufacturing stage;

FIG. 3 shows the ballast of FIG. 2 including a housing intersected alongthe longitudinal axis and a device for filling said ballast with amoulding mass;

FIG. 4 shows a detail of the ballast of FIG. 3 on a larger scale;

FIG. 5 shows the same detail as in FIG. 4 during a followingmanufacturing stage;

FIG. 6 is a cross-section taken on the line VI-Vl of the ballast of FIG.3;

FIG. 7 shows the same cross-section as in FIG. 6 during a followingmanufacturing stage;

FIG. 8 shows another embodiment of the synthetic resin block for aballast according to the invention as well as part of the cover for thehousing of said ballast;

FIG. 9 shows the same part of FIG. 8 during a following manufacturingstage;

FIG. '10 likewise shows the same ballast of FIGS. 8 and 9 during a stillfurther manufacturing stage.

In FIG. 1 the reference numeral 1 denotes a cover for an inductiveballast for stabilizing a low-pressure mercury vapor discharge lamp.FIG. 2 is a perspective view of the other parts of this housing and itscontents namely a coil for this housing. The cover 1 which is shown inFIG. 1 consists of steel having a thickness of approximately 0.8 mm. Thereference numerals 2, 3, 4 and 5 denote holes for connecting said coverduring a further manufacturing stage with the other parts of the housingwhich are shown in FIG. 2. The reference numerals 6 and 7 denoteassembly holes for securing the complete housing to a longitudinal bar,for example, a lighting fixture.

In FIG. 2 the reference numeral l0 shows the trayshaped part of thehousing. The reference numerals 1 1, l2 and 13 show connecting holeswhich correspond to the holes 2, 3 and 4 of FIG. 1. A fourth hole in thetrayshaped housing is not visible in FIG. 2 because a part of this tray10 in this Figure is cut away. The trayshaped housing 10 includes a coilwhich consists of a number of laminations 14 and an electrical winding15. The laminations 14 are E-shaped and are formed in two packs.

The electrical winding 15 is provided with two electrical connectingconductors l6 and 17. These connecting conductors are passed to theexterior through the wall of the housing 10 and terminate in connectionpins. Only one of these pins (reference numeral 18a) is shown in FIG. 2.Reference numeral 18a denotes the pin which is in electrical contactwith the connecting conductor 17. A flat insulating plate 18 is providedbetween the connecting conductors l6 and 17 at one end and thelaminations 14 at the other end is placed on top of the connectingconductors l6 and 17, which block is provided with closed cells. Thismeans that block 19 includes a (large) number of compartments which arenot in communication with the outside air. This block may consist of,for example, synthetic rubber and may have a volume of approximately 1.5cubic/ems. The side of the synthetic resin block 19 remote from theconnecting conductors 16 and 17 is denoted by the reference numeral 20.This part is provided with a layer which cannot substantially stretch.This layer consists of, for example, a polyester foil. FIG. 2 shows aballast for stabilizing the arc in a low-pressure mercury vapordischarge lamp and this during a given manufacturing stage. The coil aswell as the tray-shaped housing 10 is completely finished in this case.The synthetic resin block 19 is already placed on the connectingconductors l6 and 17.

The next stage is to place the cover 1 (see FIG. 1) on the tray-shapedpart 10 of the housing (see FIG. 2) and this in such a manner that theholes 2 and 11, and 3 and 12, and 4 and 13 coincide with each other.

FIG. 3 shows the box-shaped ballast thus manufactured and now beingprovided with a cover. The reference numerals in FIG. 3 correspond tothose of the previous Figures. In FIG. 3 the housing 10 is shown in acompartment 30. This compartment is connected at one end to a reservoir31 which is filled with a liquid polyester mass and at the other end toa vacuum pump 32. The supply lead from the reservoir 31 to thecompartment 30 includes a valve 33. The connection between compartment30 and vacuum pump 32 includes a valve 34. The compartment 30 has aclock-shaped wall 35 and a base 36. A plate 37 is provided between thehousing 10 and the base 36 of compartment 30. The base 36 and the plate37 can be moved up and down in a manner not further shown. As a resultcompartment 30 can be opened or closed. In the situation shown in FIG. 3the compartment 30 is closed. The reference numerals 38 and 39 denoteseals so as to shut off the compartment 30 in an airtight manner fromthe outside atmosphere. The supply pipe 40 protrudes through the hole 8in the cover 1 of the ballast (see also FIG. 1 for this hole). Referencenumeral 41 denotes a seal by which polyester mass is prevented fromgetting between the ballast and the wall of the compartment.

The ballast is introduced into the compartment by firstly lowering thebase 36, subsequently placing the ballast on the plate 37 and thenraising the base 36 up to the position shown in FIG. 3. Referencenumeral 19 again denotes the block of synthetic resin material.

When valve 42 is closed, valve 34 is opened and vacuum pump 32 isstarted. As a result the compartment 30 is substantially evacuated andhence, through chinks which are still present in the ballast, also theinterior of this ballast. As a result the synthetic block 19 in theballast will swell and envelops the connecting conductors, inter alia,17. Subsequently valve 33 is opened. Due to the pressure belowatmospheric pressure which prevails in the ballast the polyester mass issucked in and flows to all parts of the ballast. As a result thepressure in the ballast will also increase to some extent. The polyestermass also moves about the synthetic resin block 19. When the entireballast is filled with polyester mass, valve 33 and also valve 34 areclosed and valve 42 which is in communication with the outsideatmosphere is opened. As a result the interior of the compartment 30reaches its normal atmospheric pressure again. Subsequently the base 36is lowered and the finished ballast is removed from the plate 37. Theblock 19 then surrounds the connecting conductors l6 and 17 with thepolyester mass surrounding the resin. After a period of waiting thepolyester mass will have hardened and the ballast is ready for furthertransport and for use as a ballast for a discharge lamp. If desired, aplurality of ballasts instead of one ballast can be treatedsimultaneously in one compartment to be evacuated.

To illustrate the situation with reference to the synthetic resin block19 more clearly, FIG. 4 shows the top-right part of the housing of FIG.3 on a large scale. Also in this case the reference numerals are againthe same as those in the previous Figures. FIG. 4 shows the situationprior to evacuation of the compartment 30 of FIG. 3 and FIG. 5 shows thesame detail as in FIG. 4 but after the compartment 30 has beenevacuated. It can be seen that in the case of FIG. 5 the synthetic resinblock 19 has swollen and even extends to below the connecting conductor17. It will be apparent from FIGS. 6 and 7 how the elastic block 19 ofsynthetic resin moves about the connecting conductors l6 and 17. TheseFigures are right-hand side elevational views of the housing 10 of FIG.3, with the right-hand side wall being omitted. FIG. 6 shows a situationcomparable to that of FIG. 4, namely the situation prior to evacuationof compartment 30. FIG. 7 shows a situation comparable to FIG. 5 namelyafter evacuation of compartment 30 (see FIG. 3). Prior to evacuation(see FIG. 6) the synthetic resin block had the original dimensions (seeFIG. 2). After evacuation this block had swollen and envelops theconductors l6 and 17. Due to the non-stretchable layer a given curvatureon the side of the block 19 facing the connecting conductors wasobtained so that at the area of the insulating plate 18 (see FIG. 5) asatisfactory urging of these conductors is obtained while the syntheticresin block has entirely enveloped the connecting conductors between theplate 18 and the pin 18a.

FIG. 8 shows a further embodiment of the synthetic block. This block isdenoted by reference numeral 50.

The upper side also includes a substantially nonstretchable layer 51.The reference numerals 52 and 53 vdenote connecting conductors which arecomparable to 16 and 17 of FIG. 2. The synthetic resin block 50 differsfrom block 19 by the presence of the two grooves 54 and 55 whosedistance is substantially equal to that of the connecting conductors 52and 53. The reference numeral 1 denotes a part of the cover for thehousing of the ballast. When this block 50 was used instead of block 19of FIG. 3, it would assume the shape upon evacuation as shown in FIG. 9.As a result of swelling and by the presence of the substantiallynon-stetchable layer 51 the grooves 54 and 55 open. Due to this swellingthe grooves will accommodate the conductors 52 and 53. If subsequentlythe polyester moulding mass flows into the housing, which is entirely inaccordance with what has been described with reference to FIG. 3, thepressure on the block will also again become approximately the same asthe atmospheric pressure and the two grooves 54 and 55 will close sothat the connecting conductors 52 and 53 are very satisfactorilyenveloped.

The ballasts described will not damage the conductors, even in case ofshrinkage cracks in the moulding mass.

What is claimed is:

l. A method of making an inductive ballast having a housing, a coilwithin the housing, and electrical conductors for connection of the coilcomprising the steps of placing a block of elastically deformablesynthetic resin having closed cells within the housing on saidconductors, closing said housing so that the space between saidconductors and the adjacent wall of said housing is substantially filledwith said block, evacuating the interior of said housing sufficiently sothat as a result of pressure developing within said cells, saidelastically deformable block swells and envelops each of saidconductors, filling the interior of said housing with a liquid resin,and allowing said resin to harden.

2. The method according to claim 1 further comprising the step ofproviding a support for said conductors on the side of said conductorsremote from said block, and providing said block on the side thereofremote from said conductors with means to prevent swelling thereof.

3. The method according to claim 1 further comprising the steps offorming a plurality of grooves in one side of said block in a directionparallel to said conductors so that upon evacuation of said housing andswelling of said block said grooves will open so as to accommodate saidconductors, said grooves being closed to encapsulate said conductorsupon filling said housing with said resin, and providing means on saidblock on the side thereof remote from said conductors for preventingswelling of said side so that the side having said grooves will becurved upon expansion.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3903223 DATED September 2, 1975 INV ENTORUQ 3 JAN LAMBERTUSVAN DER HGEK It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 64, after "at the other end" insert An elasticallydeformable block,

preferably of synthetic resin material,--

Column 4, line 10, delete "and this" Column 5, line 1, after"surrounding the" delete "resin" and insert -block of synthetic resin.-

Signed and Scaled this ninth Day of December 1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uj'Patentsand Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OFCORRECTION PATENT NO. 1 3903223 DATED September 2, 1975 INVENTORO?) IJAN LAMBERTUS VAN DER HOEK It is certifi ed that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below: v

Column 3, line 64, after "at the other end" insert An elasticallydeformable block, preferably of synthetic resin material,

Column 4, line 10, delete "and this" Column 5, line 1, after"surrounding the" delete "resin" and insert block of synthetic resin.

Signed and Sealed this ninth D3) of December 1975 [SEAL] Attest:

& RUTH C. MASON C. MARSHALL DANN AIIPSH'RL ffi (nmmissioner ufPatenrsand Trademarks

1. A METHOD OF MAKING AN INDUCTIVE BALLAST HAVING A HOUSING A COILWITHIN THE HOUSING, AND ELECTRICAL CONDUCTORS FOR CONNECTION OF THE COILCOMPRISING THE STEPS OF PLACING A BLOCK OF ELASTICALLY DEFORMABLESYNTHETIC RESIN HAVING CLOSED CELLS WITHIN THE HOUSING ON SAIDCONDUCTORS, CLOSING SAID HOUSING SO THAT THE SPACE BETWEEN SAIDCONDUCTORS AND THE ADJACENT WALL OF SAID HOUSING IS SUBSTANTIALLY FILLEDWITH SAID BLOCK, VACUATING THE INTERIOR OF SAID HOUSING SUFFICIENTLY SOTHAT AS A RESUL T OF PRESSURE DEVELOPING WITHIN SAID CELLS, SAIDELASTICALLY DEFORMABLE BLOCK SWELLS AND ENVELOPS EACH OF SAIDCONDUCTORS, FILLING THE INTERIOR OF SAID HOUSING WITH A LIQUID RESIN,AND ALLOWING SAID RESIN TO HARDEN.
 2. The method according to claim 1further comprising the step of providing a support for said conductorson the side of said conductors remote from said block, and providingsaid block on the side thereof remote from said conductors with means toprevent swelling thereof.
 3. The method according to claim 1 furthercomprising the steps of forming a plurality of grooves in one side ofsaid block in a direction parallel to said conductors so that uponevacuation of said housing and swelling of said block said grooves willopen so as to accommodate said conductors, said grooves being closed toencapsulate said conductors upon filling said housing with said resin,and providing means on said bLock on the side thereof remote from saidconductors for preventing swelling of said side so that the side havingsaid grooves will be curved upon expansion.